Google Groups email
Below is an email (in the email it is HTML so it looks nicer) that is sent out when a request for Google Classroom is approved. Fred or G Suite Admin has to approve request so they may come much later than the request is submitted. The email looks fake but is a legit email.
From: Classroom Teachers
Google Groups Logo for Google Groups Congratulations, your request to join the Classroom Teachers group was approved by a group moderator. Get started with your new group Google Groups allows you to create and participate in online forums and email-based groups with a rich community experience. You can also use your Group to share documents, pictures, calendars, invitations, and other resources. Learn more.
Visit the group Visit the help center.